1. Field of the Invention
The present invention relates to the field of magnetic resonance imaging and more specifically to measurement of fluid flow with magnetic resonance.
2. Description of Related Art
Components of fluid motion, such as velocity and acceleration are important parameters to measure in many systems. These parameters are useful in determination of development of vascular diseases such as arteriosclerotic disease.
A traditional fluid flow analysis method, known as ink streamlining, requires introducing a contrast agent into a flowing fluid and observing the motion of the contrast agent.
Another method of measuring motion of materials employs laser Doppler technique. This requires a laser beam to be reflected from particles suspended in the material which is to be measured, and determining the displacement of each particle over a short interval thereby indicating the velocity of the material at the chosen location. Neither ink streamlining or laser Doppler methods are suitable for the detection of velocity within blood vessels.
An alternative method for the measurement of velocity in moving fluids within a vessel relies on Doppler shifts in reflected ultrasound signals. With this method, an ultrasound probe is placed near the vessel. Ultrasonic waves are transmitted into the vessel and reflected by the fluid. As the fluid moves, the frequency of the reflected ultrasonic waves is changed. For fluid moving towards the ultrasound probe, the reflected waves have a higher frequency, while reflected waves from fluid moving away from the probe have a lower frequency.
Ultrasonic measurement methods, however, are limited by the ability of the system to measure only the component of velocity directly to, or away from, the probe; and are limited by the need for the vessel to be surrounded by tissue which is transparent to ultrasonic energy.
A number of methods for the detection and measurement of fluid motion with magnetic resonance have been previously disclosed. These methods employ motion sensitive MR pulse sequences to identify the moving fluids.
There is a need for a simple method of determining components of fluid motion employing magnetic resonance.